1. Field of Invention
This invention relates to versatile active microbiocides which provide durable protection for composite roofing products.
2. Description of the Prior Art
Technical advances in the manufacture of residential roofing are being compromised by increasing maintenance requirements and environmental threats posed by the products in the marketplace. These problems are associated with unsightly algae growth on both concrete tile and asphalt shingle roofs which dominate the market. Most severe in warm moist climates, algae proliferation due to storm turbulence, high density planned communities and manufacturing processes gives cause for alarm considering the inherent transient uncontrollable algae inhibitors on which the technology is established. Evidence of viable alternatives to achieve projected product life and avoid service requirements is lacking in these industry segments. The prevailing conventional wisdom would deny the most fundamental observations regarding the nutrient value of calcium carbonate in sustaining autotropic biological growth and the threshold lethal dosage of ionic divalent metal compounds. And the increasing incidence of warranted product failures and pro-rated remedies can only be reconciled by loss of manufacturer identity in the marketplace.
Historically, the concrete tile industry has represented the high end roofing product in terms of esthetics, prestige, structural requirements and cost. The system relies on the integral granular surfaced roll roof which the tile serve to protect for traditionally forty year roof life. Concrete tiles, produced from a range of processes and compositions, were the first to evidence unacceptable roof discoloration and actually spawned the now mature cleaning and painting service sector. While this industry has not actively pursued algae inhibition per se, efforts to reduce efflorescence through the use of sealants and coatings have provided some measure of relief. Cast tile products retain relatively high moisture to support algae growth and typically quality for maintenance cleaning service the year of installation. Extruded tile are more consolidated and are optionally sealed and surfaced coated. The application of internal sealant is intended to reduce moisture intrusion as the source of efflorescence and initial algae discoloration is slower to develop. Improvements achieved with supplemental glaze coatings can extend maintenance free life to approximately 7 years. Ultimate loss of the surface coatings by weathering qualifies the roof for routine cleaning maintenance with accompanying reduction in product life. Mechanical fastening versus masonry or foam adhesives used to secure tiles also effect moisture retention and algae growth in these systems. Growing attention to algae discoloration in southern markets has prompted an increased use of heat absorbing dark colors and replacement of tile with the shorter life asphalt shingle roof. In addition, home owner associations increasingly enforce maintenance standards with little or no substantive information on the damage incurred by the service.
In contrast the asphalt shingle industry records early concern for the algae discoloration with studies on characterization and algae resistance (AR) technology. The composite roll product also used in the tile roofing system is produced on high speed web lines in which a base mat is saturated with molten asphalt and surfaced with ceramic coated granules which are embedded by roll pressing. This product is optionally cut on line for either three-tab or laminated shingles. AR products incorporating zinc and/or copper oxide modified admixtures with ceramic surface granules is widely practiced as an extension of current manufacturing technology. Evidence of water soluble ionic salt derivatives being the active microbiocides from these relatively inert source materials is commonly held by those skilled in the art, although the physical and chemical requirements to effect the conversion are typically misrepresented. Narayan et. al. (U.S. Pat. No. 5,356,664) describes incorporation of copper oxides in the ceramic protective coatings of granules as a source of this type microbiocide. Physically, formation of dew and absorption of sulfur and nitrogen oxides to yield a pH of 6.5-5.5 is prerequisite to acid displacement of the insoluble covalent bound copper in a heterogeneous interfacial surface reaction. Bond cleavage with concomitant loss of electrons in two steps yields divalent cupric cation in balance with acid anion as water soluble salt. Once released, diffusion away from the source in thermodynamic equilibration of concentration throughout the moisture film competes with the dynamics of drainage from the roof. The typical constricting pattern of inhibition trailing from metal components on residential roofs evidences an infinitesimal concentration gradient associated with dilution and drainage of soluble salt. This transient nature of the inhibitor combined with the site specific chemical requirements for its release belie general efficacy. And with regard to cupric oxide containing granules, inaccessibility within the ceramic protective coating and asphalt adherent create gross chemical inefficiencies. Exacerbating this situation, has been the industry's increased use of calcium carbonate filler in asphalt formulations which has reduced AR products' maintenance free life to approximately to 1.5 years with lower end products. The trends in increased cleaning maintenance and use of dark color products are disturbing, particularly as in-roads to high end cement tile markets continue. Notwithstanding the numerous processing variants and trade secrets, the industry relies on a common AR technology which is inconsistent with performance claims. Given esthetics as the traditional driving force for product standards, the modification of ceramic coated granule processing for asphalt roof protection has lead to the present duplicity. Thus, this critical component of residential construction is becoming the highest maintenance and primary structural replacement item of the home.